1. Field of the Invention
The present invention relates to an optical scanner unit and an image forming apparatus incorporating the same such as a digital copier, a laser printer, or a laser facsimile machine.
2. Description of the Related Art
It is well known that such an image forming apparatus comprises an optical scanner unit which includes a light source made of laser diodes (hereinafter, LD) or the like and a deflector to deflect a light beam from the light source to scan the surface of an image support member with the light beam and generate an electrostatic latent image. The optical scanner unit of this type includes a synchronous detector which receives a part of the light beam deflected by the deflector when scanning, detects a write start position in main scan direction on the image support member, and feeds back the detected information to control the LD.
However, there is a problem in the prior art optical scanner unit that the light source may fail to regularly emit a light beam due to incidence of light on the LD which has been reflected by the light receiving face of the synchronous detector or a case thereof. This may cause a problem of generation of non-normal images.
In order to solve the problem, Japanese Unexamined Patent Application Publication No. Hei 11-95138 proposes an optical scanner unit which is configured to include a housing with a convex to position a synchronous detector and a circuit board with a concave on which a synchronous detector is mounted so that the synchronous detector is fitted into the housing.
In this optical scanner unit, the synchronous detector can be positioned securely, however, it is still possible for a light beam reflected by the synchronous detector to be incident on the LD since the angle at which the synchronous detector is fixed is not restricted.
Japanese Unexamined Patent Application Publication No. 2007-148356 discloses another optical scanner unit which is configured to control the LD not to turn on when a light beam from the LD is incident on the mirror face of the deflector at 90 degree angle, thereby preventing a returning light from the deflector from being incident on the LD.
However, there still remains a possibility that a returning light from the synchronous detector may be incident on the LD immediately before turning-off of the LD since the angle at which the synchronous detector is fixed to the housing is not restricted.